Purpose: Testicular volume measurements obtained with the Prader and Rochester orchidometers were compared to those obtained using scrotal ultrasound. The ability of each orchidometer versus ultrasound in detecting volume differential between 2 testes and the accuracy of orchidometer measurement by a less experienced examiner to that of a urologist were compared. Materials and Methods: A total of 65 males were examined by the attending urologist and urology nurse using the Prader and Rochester orchidometers, and scrotal ultrasound was subsequently performed by an attending radiologist. Statistical analysis of the results was performed to determine the correlation of orchidometer measurements between examiners, as well as with ultrasound, and sensitivity and specificity of orchidometer and ultrasound in detecting defined volume differentials between testes of 10%, 15%, 20% and 25%. Results: There was a strong linear relationship between testicular volume measurements using either orchidometer and ultrasound. To detect a defined volume differential as determined by ultrasound orchidometer sensitivity was weak, whereas orchidometer specificity was better. There was a strong correlation between orchidometer measurements of the urology nurse and attending urologist. Conclusions: Although the orchidometer remains valuable in assessing size of the individual testis, it is too insensitive to volume differentials relative to ultrasound to be used routinely to determine growth impairment. For this reason observation of an adolescent with varicocele should include an annual ultrasound assessment of testicular volume.
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